The present invention relates to a process for regenerating a poly(1-trimethylsilyl-1-propyne) membrane. More particularly, the present invention relates to a process for regenerating a poly(1-trimethylsilyl-1-propyne) membrane used in a pervaporation process for recovering volatile organic compounds such as n-butanol from aqueous solutions and/or fermentation broths.
It is known that membranes comprised of glassy polymers such as poly(1-trimethylsilyl-1-propyne) (PTMSP) are highly effective in the separation of volatile organic compounds such as n-butanol from aqueous liquid streams and fermentation broths such as acetone butanol ethanol (ABE) fermentation broths in a pervaporation process.
Pervaporation is a common separation technique wherein liquid volatile organic compounds such as n-butanol are preferentially transported and separated across a thin membrane film supported by a porous support structure which provides mechanical strength. The feed side of the membrane is contacted by the aqueous liquid containing the volatile organic compound, while a vacuum or sweep gas is applied on the permeate side of the membrane as a driving force to selectively transport components of the liquid through the membrane. The volatile organic compounds are collected on the permeate side of the membrane by condensation in a cold trap. Two characteristics of the PTMSP membrane define the membrane""s effectiveness in the separation of volatile organic compounds such as n-butanol in a pervaporation process: selectivity toward the desired species to be separated and flux or flow rate of the desired species through the membrane. Flux is generally defined as the rate at which desired products contained in a feed solution pass through the membrane and is generally reported in g/m2h.
When separating n-butanol from an aqueous solution a fermentation broth selectivity is defined as the ratio of the butanol:water concentration of the permeate to that of the retentate:
selectivity=permeate(Cbutanol/Cwater)/retentate(Cbutanol/Cwater)
where the permeate is what crosses the membrane and the retentate is the feed solution concentrate, or what is retained on the feed side of the membrane and recirculated to the feed tank. Higher selectivity translates into a more pure permeate with higher separation efficiencies.
In a pervaporation process utilizing a PTMSP membrane, there are two separate steps involved in the removal of volatile organic compounds such as n-butanol from an aqueous solution or fermentation broth. The first step involves the sorption of the volatile compound into the membrane. The second step is the diffusion of the volatile through the membrane due to a driving source such as a vacuum which creates a concentration gradient. To enhance membrane performance and increase efficiency, selective sorption of the volatile must be increased and/or diffusion resistance must be reduced, or both.
Although PTMSP membranes are highly effective in recovering n-butanol from aqueous solutions or fermentation broths due their high selectivities and high flux rate, these advantageous characteristics deteriorate over time as the membrane becomes fouled and/or compacted. This deterioration occurs quickly in the presence of ABE fermentation broth and the membrane becomes unsuitable for use within a short period of time. Because constantly replacing fouled PTMSP membranes is cost-prohibitive and time consuming, a need exists for a simple method of cleaning or regenerating PTMSP membranes such that a single membrane may be cleaned or regenerated and reused numerous times.
Among the objects of the present invention, therefore, are the provision of a simple, cost-effective process for regenerating a fouled PTMSP membrane; the provision of using a butanol-containing liquid as a washing agent to clean and regenerate a fouled PTMSP membrane; the provision of a process for increasing the efficiency of butanol separation from fermentation broth or an aqueous stream using a PTMSP membrane; and the provision of a process for regenerating a fouled PTMSP membrane utilizing a product stream separated by the membrane.
Briefly, therefore, the present invention is directed to a process for regenerating a poly(1-trimethylsilyl-1-propyne) membrane having a feed side and a permeate side. The process comprises contacting the feed side of the membrane with an aqueous cleaning solution containing at least about 50% by volume butanol.
The invention is further directed to a separation process utilizing a poly(1-trimethylsilyl-1-propyne) membrane having a feed side and a permeate side. The process comprises contacting the feed side of the membrane with a feed solution containing a volatile organic compound while applying a driving force across the membrane to cause components of the feed solution to permeate the membrane and form a permeate having an organic phase and an aqueous phase. The membrane is regenerated by contacting the feed side of the membrane with an aqueous cleaning solution containing at least about 50% by volume butanol
The invention is further directed to a separation process utilizing a poly(1-trimethylsilyl-1-propyne) membrane having a feed side and a permeate side. The process comprises contacting the feed side of the membrane with a feed solution comprising ABE fermentation broth while applying a driving force across the membrane to cause components of the feed solution to permeate the membrane comprised of an organic phase and an aqueous phase until the flux of the membrane has decreased by about 50% of its original. Next, the feed side of the membrane is contacted with a pre-cleaning solution to remove any debris or media from the feed side. Finally, the feed side of the membrane is contacted with a cleaning solution containing at least about 80% butanol in water by volume to cause the cleaning solution to permeate the membrane.
Other objects and features of this invention will be in part apparent and in part pointed out hereinafter.